This application claims the priority of German Patent Document No. DE 101 35 327.8, filed Jul. 19, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to methods for changing gear in an automated change-speed gearbox of a motor vehicle and to an automated change-speed gearbox.
EP 0 695 665 B1 describes a control system for a gearbox with a servo device, which is assigned to an engine of a motor vehicle. The control system has an actuating device, which can be actuated to select and disengage a gear, perform a gear selection, and engage and disengage a clutch. The engine has a first processing unit, which regulates the torque provided by the engine and the rotational speed of engine.
A second processing unit of the control system is suitable, in the case of a gear change from an original gear to a target gear, in particular during a downshift, for supplying control information to the first processing unit of the engine before the disengagement of the original gear to bring about a controlled reduction of the torque provided by the engine. Before the target gear is selected, the first processing unit supplies the second processing unit with further control information in order to bring a rotational speed of the engine to a given target value. During this process, the clutch is either closed for the entire time or it is opened before the original gear is disengaged and is completely closed after the original gear is disengaged.
DE 198 59 458 A1 discloses a gearbox in the form of a change-speed gearbox. The gearbox has a shiftable drive-away clutch arranged on the input side and additional clutches, in particular power-shift clutches, which engage gearwheels with a shaft. It also describes a method for changing from an original gear to a target gear, in particular for downshifting. The gear change is carried out without control of engine torque. After the start of shifting, a power-shift clutch is closed. When the power-shift clutch is transmitting the full torque, the original gear can be deselected. A gearbox input shaft is then brought to a higher target rotational speed. As soon as the target rotational speed has been reached, the target gear is selected. The drive-away clutch remains closed during the entire shift operation or is opened during the deselection of the original gear and the selection of the target gear.
In view of the prior art, it is an object of the present invention to provide an automated change-speed gearbox and methods for changing gear in such a gearbox, to provide smooth operation of the automated change-speed gearbox and particularly short shifting times for downshifts.
This object is achieved by the embodiments of the present invention described hereinafter.
In the case of a method according to the invention for shifting down from an original gear to a target gear, an automated clutch arranged between the engine and the change-speed gearbox is engaged up to, at most, a slip limit to increase the rotational speed of an input shaft of the change-speed gearbox.
During a downshift, the input shaft of the change-speed gearbox must be brought to a synchronization speed of the target gear, which is greater than the rotational speed of the input shaft in the original gear. The synchronization speed is achieved when a selector element of the target gear and a gearwheel of the target gear are at the same rotational speed. The input shaft is accelerated by a torque provided by the driving engine. For this purpose, the clutch arranged between the driving engine and the change-speed gearbox must transmit a torque. The clutch is engaged up to, at most, the slip limit by an actuator. The slip limit is reached when the clutch cannot transmit more than the torque applied and would thus slip if there were a very slight increase in the torque. It is particularly advantageous if the clutch is operated precisely at the slip limit. In this case, the rotational speed of the driving engine and that of the input shaft of the change-speed gearbox are identical.
This allows particularly smooth operation of the change-speed gearbox since torque peaks of the engine which occur are not transmitted to the change-speed gearbox. Moreover, torque surges, which are introduced from the road via driven wheels, are not taken by the driving engine but lead to slipping of the clutch.
In the method according to the invention for shifting down in an automated change-speed gearbox with just one automated clutch arranged between the engine and the change-speed gearbox, the clutch is at least partially disengaged to deselect the original gear. The change-speed gearbox does not have any other clutches, in particular power-shift clutches. To deselect the original gear and hence release a selector element of the original gear from a gearwheel of the original gear, only a very low torque must be transmitted from the selector element to the gearwheel or vice versa. The clutch can, for example, be opened only until the absolute value of the torque at the selector element of the original gear has undershot a threshold value. The torque at the selector element can be calculated by a control device that carries out the method according to the invention. Calculation can, for example, take place on the basis of the torque provided by the engine, the rotational speeds and the rotational-speed time derivative of the individual shafts in the change-speed gearbox and physical parameters, e.g. the mass moment of inertia, of individual components or subassemblies of the change-speed gearbox. The clutch can be disengaged by a ramp or by a predetermined characteristic or abruptly, for example.
The rotational speed of the engine is adjusted in the direction of the synchronization speed of the target gear simultaneously with the opening of the clutch. Adjustment can be accomplished by control and/or regulation of the rotational speed and/or of the torque provided by the engine. After the deselection of the original gear, the clutch is at least partially reengaged in order to match the rotational speed of the input shaft of the change-speed gearbox to the rotational speed of the engine and hence increase it.
This leads to particularly short shifting times for a downshift since the input shaft of the change-speed gearbox reaches the synchronization speed of the target gear particularly quickly, and the target gear can thus be selected particularly quickly. Any interruption in the tractive effort at the vehicle wheels during the shift is thus particularly short.
In addition, a considerable reduction in the cost of the change-speed gearbox is achieved by the elimination of power-shift clutches.
In another method according to the invention, the clutch is disengaged to deselect the original gear, ensuring torque can no longer be transmitted by the clutch. For the deselection of the original gear and hence for the release of a sector element of the original gear from a gearwheel of the original gear, only a very low torque must be transmitted from the selector element to the gearwheel or vice versa. If this is achieved by disengaging the clutch, the original gear can be deselected without the possibility that torque surges will be introduced into the motor vehicle. This allows smooth operation of the motor vehicle.
In yet another method according to the invention, the clutch is partially disengaged to deselect the original gear. The clutch is disengaged only until a selector element of the original gear can be disengaged.
In still yet another method according to the invention, the rotational speed of the engine is adjusted in the direction of the synchronization speed of the target gear simultaneously with the disengagement of the clutch. This allows particularly short shifting times since the engine and, after the partial engagement of the clutch, the input shaft of the change-speed gearbox, reach the synchronization speed in as short a time as possible. The target gear can thus be selected after a particularly short time.
In a further method according to the invention, the change-speed gearbox is embodied as a non-synchromesh (claw-type) shift gearbox. Change-speed gearboxes of this kind do not have synchronizing devices, e.g. synchronizer rings. For this reason, there must be approximate equality between the rotational speeds of a selector element of a gear to be selected and the gearwheel of the gear to be selected before the selector element is actuated by an actuator. In the case of downshifts, this can be achieved by the engine. In the case of upshifts, a gearbox brake can be employed or it is necessary to wait until equality between the rotational speeds is established due to friction in the change-speed gearbox.
Such gearboxes can be produced in a simple manner and with a small number of components compared with synchromesh shift gearboxes. This enables a gearbox of this kind to be produced at low cost.
In a yet further method according to the invention, adjustment of the rotational speed of the input shaft of the change-speed gearbox into a range around the synchronization speed of the target gear takes place in two phases. In the first phase, at the beginning of adjustment, the rotational speed rises very rapidly, i.e., the time derivative of the rotational speed is large. As soon as the difference between the synchronization speed and the rotational speed of the input shaft has undershot a threshold value, the second phase of adjustment begins.
In the second phase, the rotational speed of the input shaft no longer rises as sharply, i.e. the time derivative is smaller than in phase one. The rotational speed of the input shaft can thus be adjusted very accurately to the synchronization speed. As a result, the target gear can be selected without torque peaks being introduced into the vehicle. This leads to particularly smooth selection of the target gear.
In a still further method according to the invention, the clutch is engaged beyond the slip limit after the adjustment of the rotational speed of the input shaft of the change-speed gearbox into a range around the synchronization speed of the target gear. On completion of the gear change, the clutch must be fully reengaged in order to be able to transmit the torque of the engine. If engagement beyond the slip limit takes place already after the adjustment of the rotational speed of the input shaft of the change-speed gearbox into a range around the synchronization speed of the target gear and hence just before the selection of the target gear, the torque can be transmitted immediately after the selection of the target gear. This leads to a particularly short interruption of the tractive effort at the driven wheels.
In a still yet another method according to the invention, there is at least one further (intermediate) gear between the original gear and the target gear, the intermediate gear being selected in the case of a gear change from an original gear to a target gear. If the clutch is engaged up to, at most, the slip limit to increase the rotational speed of an input shaft of the change-speed gearbox, torque peaks that could occur during the selection of the intermediate gear are not taken by the driving engine. Instead, the clutch slips and the occupants of the vehicle cannot feel the torque peaks. This allows particularly smooth operation of the change-speed gearbox.
In another method according to the invention, the adjustment of the rotational speed of the input shaft of the change-speed gearbox into a range around the synchronization speed of the intermediate gear takes place in just one phase. The rotational speed of the input shaft is increased very quickly and the range around the synchronization speed is therefore reached after only a short time. This advantageously allows particularly short shifting times.
In an automated change-speed gearbox according to the invention, an automated clutch is arranged between the engine and the change-speed gearbox. The change-speed gearbox has a control device, which comprises at least one clutch control device that engages the clutch up to, at most, the slip limit during a downshift from an original gear to a target gear to increase the rotational speed of the input shaft of the change-speed gearbox.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.